Field of the Invention
The invention relates to a secondary-side residual-heat removal system for a pressurized-water nuclear reactor, including a steam generator being connected into a primary loop of the nuclear reactor by the primary side of its heat-exchanging tubes, and a safety condenser having one side to which a secondary side of the steam generator is connected through circuit lines, with another (tertiary) side of the safety condenser allowing a throughflow of a tertiary medium for the cooling of its secondary side, and the safety condenser being situated at a higher level than the steam generator, defining a difference in level between the safety condenser and the steam generator being dimensioned for achieving a natural circulation in a secondary circuit leading through the secondary side of the steam generator and the safety condenser in a residual-heat removal operation.
After shutting down nuclear reactors, so-called residual heat, which is also referred to as decay heat, occurs in all modes of operation and malfunction. In the case of pressurized-water nuclear reactors, the secondary side is used, at least in an initial phase, for the removal of the residual heat, in virtually all modes of operation and malfunction. That takes place by feeding the steam generators with feed-water and by discharging energy transferred in the heat generator from its primary side to its secondary side through its tube bundle, directly or indirectly into the atmosphere.
In order to keep malfunctions under control, a previously known concept for secondary-side residual-heat removal in the installations of pressurized-water nuclear reactors provides an emergency feeding system on the secondary-side feeding side of the steam generators and a steam blow-off device with blow-control and a safety valve on the discharge side. Such a system is disclosed, for example, by German Published, Prosecuted Application DE-AS 24 59 150 (1) or by Published European Application No. 0 004 167 A3 (2). In publication (1) it is shown that the respective heat generator is connected by its secondary side not only to its operational feed-water and live-steam lines but also through emergency cooling circuit lines with a condensate recirculation pump to one side of a safety condenser. That safety condenser, which is referred to therein as a residual-heat removal heat exchanger and is equipped with additional condensate cooling means, may be replaced, if appropriate, by a water pool basin. Such a basin is shown in publication (2) and it serves for the blowing off of the secondary-side steam to be cooled, with the water pool being cooled by heat-exchanging tubes which are connected to a cooling circuit. The secondary-side steam is cooled and condensed by the blowing off into the water pool. The condensate is recirculated by means of a condensate recirculation pump to the secondary side of the steam generator, i.e. to its feed-water space. In the case of publication (1) and publication (2), residual-heat removal operation is initiated by the opening of conventional shut-off valves (reducing valves, shut-off valves).